Limitations of Northern Blotting: What It Cannot Determine

In traditional Northern blotting technique, which one of the following types of information cannot be determined.
A. Half-life of an mRNA
B. Amino acid sequence of the protein coded by an mRNA species
C. Strand of DNA that is transcribed into an mRNA
D. Size of an mRNA species

The Northern blotting technique is widely used in molecular biology to analyze RNA expression levels and determine the size of specific mRNA molecules. However, like any technique, it has its limitations. Among the options provided, the amino acid sequence of the protein coded by an mRNA species (Option B) cannot be determined using Northern blotting.

Explanation of Each Option:

1. A. Half-life of an mRNA – Can be inferred indirectly

   • Although Northern blotting alone does not measure mRNA half-life, researchers can estimate it by performing RNA stability experiments over time and analyzing mRNA degradation patterns.

2. B. Amino Acid Sequence of the Protein Coded by an mRNA Species – Cannot be determined

   • Northern blot detects RNA, not proteins.
   • The amino acid sequence of a protein is determined by translating the mRNA sequence into protein using genetic code rules.
   • To determine the protein sequence, techniques like mass spectrometry or Western blotting are required.

3. C. Strand of DNA That Is Transcribed into an mRNA – Can be determined

   • By using strand-specific probes, scientists can identify whether the coding strand (sense) or template strand (antisense) of DNA is transcribed.

4. D. Size of an mRNA Species – Can be determined

   • Northern blotting involves RNA separation by gel electrophoresis, allowing the estimation of mRNA size compared to molecular weight markers.

Conclusion:

While Northern blotting is valuable for studying gene expression and RNA size, it cannot determine the amino acid sequence of a protein encoded by an mRNA. To analyze protein sequences, other techniques like Western blotting or mass spectrometry must be used.

For accurate molecular biology research, choosing the right technique is crucial!